CMOS及P/N接面變容器在CMOS整合電路尤其是射頻電壓控制震盪器中的應用特別重要, 並且讓單晶片傳送接收器在未來變得更有經濟價值. 論文中我們討論且比較下列變容器在射頻用途中的應用: (a) the P+-to-N well junction varactor, (b) the Inversion mode MOS varactor, and (c) the Accumulation mode MOS varactor. 比較的基準主要是品質指數以及電容可調整比例(最大電容值除於最小電容值)兩項. 量測的頻率則選取無線應用最常用的頻段, 即從200 MHz到20GHz.

　　元件的製作是採用標準0.18um CMOS的製程. 我們不但量測了電容, 電阻, 以及品質指數對於電壓以及頻率的關係, 並且也提出了佈線的如何最佳化. 由實際結果吾人認為, P+-to-N well junction varactor雖然有最高的品質指數, 但是其電容可調整比例過低, 因此不敷許多實際應用所需, 而Accumulation mode MOS varactor 則兩者皆優, 是最適合於無線應用的變容器類型.

　　CMOS varactors and junction varactors as tunable capacitors are important for CMOS integration circuits especially for the voltage control oscillators (VCOs), and may enable the realization of an inexpensive single chip transceiver. Varactors for RF applications are discussed and compared in this thesis. Three CMOS varactors with different structure were characterized in detail for performing comparisons, i.e., (a) the P+-to-N well junction varactor, (b) the Inversion mode MOS varactor, and (c) the Accumulation mode MOS varactor. The evaluation is mainly based on two major performance parameters, i.e., the quality factor (Q-value) and the capacitance-tuning-ratio (Cmax/Cmin ratio). The varactors were evaluated at frequencies from 200 MHz up to 20 GHz, for the frequency range is the most interesting with respect to wireless applications.

　　These devices were fabricated in standard CMOS processes with minimum feature size of 0.18 um, and the capacitance, resistance and Q-value versus voltage and frequency curves were measured. Additionally, the layout optimization was also reported. By comparing the three evaluated varactors, the P+-to-N well junction varactor has the highest Q-value, but its Cmax/Cmin ratio is too low to apply in practice. On the other hand, the Accumulation Mode is concluded as the best-suited varactor type for wireless applications.

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